1. Technical Field
The present invention relates to a blow-by gas passage structure, and more particularly to a blow-by gas passage structure provided inside a separator chamber that is formed between a cylinder head cover and a baffle plate joined to the cylinder head cover by vibration welding.
2. Background Art
As a conventional oil mist separator, one provided inside a separator chamber that is formed between a cylinder head cover and a baffle plate joined to the cylinder head cover by vibration welding is commonly known (see, for example, JP2011-58433A). In this conventional oil mist separator, for example, as shown in FIG. 5 and FIG. 6, path-bending ribs 111 stand on the surface(s) of the cylinder head cover 102 and/or baffle plate 103 to cause the flow of blow-by gas to bend (meander) in a planar direction inside the separator chamber S. The flow of blow-by gas introduced from an inlet 105 into the separator chamber S is bent by path-bending ribs 111, and the oil components in the blow-by gas are caught through gravity sedimentation and collision. After that, the blow-by gas, from which the oil components have been separated, is discharged from the separator chamber S by a PCV valve 107 provided to an outlet 106, and transferred to the combustion chamber of the engine via an intake manifold or the like.
In the conventional oil mist separator described above, there is a gap g between the distal end of the path-bending ribs 111 and the surface of the opposing member (cylinder head cover 102 or baffle plate 103) in order to avoid interference (i.e., vibration welding) therebetween. This is because interference between the path-bending ribs 111 and the surface of the opposing member will cause the following problems. For example, burrs (foreign matter) may form after the vibration welding, or flash trap design for the vibration welding may become difficult. If the path-bending ribs 111 are high and have low rigidity, the path-bending ribs 111 may wobble largely by the vibration during the vibration welding, which may impede the heating of the resin and result in a weld failure.
Since a gap g is formed between the distal end of the path-bending ribs 111 and the surface of the opposing member for avoiding interference in the conventional oil mist separator described above, part of the blow-by gas passes through the gap g, thus creating a short-cut flow path 119. Therefore, the flow path 120 of the blow-by gas may not form as designed and intended, and the flow of blow-by gas may not be bent sufficiently, with a result that the efficiency of separating oil components in the blow-by gas is lowered.
Moreover, in the conventional oil mist separator described above, when the negative pressure inside the separator chamber S is high and when the PCV valve 107 (outlet 106) and the oil drop hole 108 are disposed close to each other, the blow-by gas is sucked into the separator chamber S through the oil drop hole 108 and flows toward the PCV valve 107. Therefore, for example, a blocking rib that blocks the flow of blow-by gas from the oil drop hole 108 toward the outlet 106 could be provided on the surface of the cylinder head cover 102 or the baffle plate 103. Even such a blocking rib would have to be formed with a gap g for avoiding interference between its distal end and the surface of the opposing member, similarly to the path-bending ribs 111 described above. Part of the blow-by gas would then pass through the gap g and thereby a short-cut flow path would be created. As a result, the effect of blocking the blow-by gas would be lowered, and the efficiency of separating oil components in the blow-by gas would also be lowered.